It is a problem in the field of sealed gauges, such as instruments, controls, instrument clusters, instrument panels, and the like, to alleviate moisture condensation from accumulating on the inner surface of the lens of these gauges when they are subjected to certain conditions. These gauges are typically formed of some type of acrylic and assembled in environments and factories that have some relative humidity, thus when they are sealed they typically contain the same relative humidity that was present during the manufacturing process for each particular gauge. In addition, when these gauges are subjected to certain environmental conditions, such as rain and cold weather, the moisture contained within the gauge forms condensation on the inner surface of the acrylic lens of that gauge and obscures or completely obstructs the view of a user to the information displayed by that gauge lens. Gauge lenses that possess a coating or are made out of a material that reduces the occurrence of moisture condensation formation during these conditions are commonly known as having anti-fog properties.
Additionally, acrylic lens provide good UV-stability relative to many of the anti-fog coatings and films presently used with other lens materials. Some attempts have been made to utilize lens substrates wholly composed of anti-fog material. However, these anti-fog materials do not typically provide good stability to UV exposure and tend to yellow and become brittle when exposed for prolonged periods of time to UV radiation, such as by repeated or constant exposure to the sun. Other attempts having been made to add LTV stabilizers to these anti-fog materials, but they still do not possess the UV stability of commonly used acrylics. Moreover, many manufacturers of vehicles that utilize these gauges require that the lens undergo extreme UV exposure testing.
In some applications, such as with automotive headlamps, the lens substrate is comprised of polycarbonate, that is prone to yellowing. Typically, to address this problem, the polycarbonate lens substrate is covered with a UV stable hard coat material to prevent yellowing of the polycarbonate lens substrate. To apply this hard coating the lens substrate material is usually spray or dip coated, which produces flow lines. Another disadvantage of dip or spray coating is that impurities that are part of the liquid coating become dried impurities of the anti-fog film once it dries. Some of these applications require 24 to 48 hours drying or curing times which exposes the coated lens to further airborne contaminates and impurities, such as dust. Other attempts have been made to alleviate or reduce moisture condensation from forming on the inner surfaces of these gauge lenses.
In one such attempt, an organic hard coat scuff-resistant layer is deposited on a release film and then pressed to one side of a flat sheet of polycarbonate and a hydrophilic organic hard coat anti-fog layer is deposited to another release film and pressed to the other side of the flat sheet of polycarbonate. The polycarbonate combination is then treated by ultraviolet (UV) radiation to cure the two coatings and the release films are then removed. The polycarbonate is then slightly bent to form such articles as shields for helmets and the like. This process provides for the polycarbonate lens substrate to be formed, deposited, and treated in flat sheets due to the nature of the process. The process does not provide for formed or shaped lenses for gauges, instruments, instrument clusters, or instrument panels. Further, the process as noted above involves a substantial number of time-consuming process steps, including preparing the two coatings, applying them to their respective release sheets, applying them to the polycarbonate substrate, pressing them to the substrate, treating with LTV radiation to cure the coatings, peeling the release films from the substrate, and possibly bending the film into a curved shape to produce a helmet visor, or the like.
Another approach to this problem has been to coat a surface of a lens substrate with a photocatalytic substance and then irradiating the coating in the presence of water to render it hydrophilic. Over time the coating loses its hydrophilic properties due to contaminants being absorbed on the surface of the hydroxyl groups of the coating surface. To restore the hydrophilicity, the coating is periodically subjected to additional photoexcitation treatments.
Yet another approach applies a coating of silicone resin to the surface of a lens substrate. Some application techniques include spraying or dip coating the lens substrate with the silicone resin. Coatings applied by dipping having only a poor-to-fair appearance, even if the parts are rotated during drippage. Additionally, coatings on vertical surfaces tend to be thicker at the bottom than at the top, which distorts the light rays emitting from the dial of the article through the lens material. Flow lines may be visible around holes and openings, and beads may develop at the bottom edges of the lens substrate. This type of process can be found in goggle manufacturing where the lens substrate is injection molded and then coated or dipped with an anti-fog compound. This process then requires that the anti-fog compound be cured or hardened, which incurs further process expense and time.
Information relevant to attempts to address these problems can be found in the U.S. Pat. No. 6,013,372 issued 11 Jan. 2000 to Hayakawa et al.; U.S. Pat. No. 6,165,256 issued 26 Dec. 2000 to Hayakawa et al.; U.S. Pat. No. 6,228,499 issued 8 May 2001 to Nakauchi; U.S. Pat. No. 6,297,906 issued 2 Oct. 2001 to Allen et al.; U.S. Pat. No. 6,303,229 issued 16 Oct. 2001 to Takahama et al.; and U.S. Pat. No. 6,830,785 issued 14 Dec. 2004 to Hayakawa et al.
Therefore, there is a need for a gauge having an embedded lens with anti-fog properties that is durable, highly hydrophilic, stable to UV-radiation, free from flow lines causes by dip or spray coating processes, affordable to manufacture, and that doesn't have or require complex processes such as UV-radiation treatment, curing or hardening steps, repeated hydrophilicity treatments, or require adhesives.
The above-described problems are solved and a technical advance is achieved in the art by the present gauge lens with embedded anti-fog. Preferably, the gauge lens comprises two layers of material, the anti-fog film and the lens substrate material, molded together to provide the gauge lens with improved weatherability, durability, and anti-fog properties. The anti-fog properties of the anti-fog film are due to its inherent chemical composition or to an anti-fog coating that is applied to the film. The anti-fog film is adjacent to the lens substrate with the anti-fog side or coating of the film facing towards the interior of the gauge. Thus, when the gauge is exposed to conditions that promote moisture condensation, the gauge lens provides an anti-fog surface for preventing the moisture from condensing onto the lens and obstructing or obscuring the view of a user.
The gauge lens with embedded anti-fog film provides a lens with improved protection from exposure to elements, such as sunlight, extreme temperatures and variances thereof, and physical stresses causes during operation of the gauge in the environment in which it is designed to operate. The gauge lens provides for improved lamination quality between the lens substrate and the anti-fog film for better Xenon arc weather ability tests. In addition, the present gauge lens design provides for a gauge lens having anti-fog characteristics that is capable of withstanding thermal shock, and physical shocks, such as vibrational shock while maintaining the bond between lens substrate material and the anti-fog film.
A manufacturing process that molds the lens substrate and anti-fog film together during the process achieves these improved features. Preferably, the anti-fog film is placed in a mold prior to injecting the gauge lens substrate material into the lens. This process ensures a strong bond between the selected anti-fog film material and lens substrate material. In addition, due to the anti-fog film being intermolded with the lens substrate at a molding temperature, impurities that are present in the mold or caused by handling the materials are vaporized and thus are not part of the finished gauge lens product. The present gauge lens also provides for a second film to be molded to the outer layer of the lens substrate material for additional durability.